Two highly sulfonated micro/mesoporous polymers, P(1,3‐DEB)‐SO3H and P(1,4‐DEB)‐SO3H, with permanent porosity, the specific surface area about 550 m2 ⋅ g−1 and the content of SO3H groups of 2.7 mmol ⋅ g−1 were prepared as new acid Porous Polymer Catalysts, PPCs. The PPCs were achieved by easy sulfonation of parent hyper‐cross‐linked micro/mesoporous polyacetylene‐type networks resulting from a chain‐growth homopolymerization of 1,3‐ and 1,4‐diethynylbenzenes. New PPCs are reported as highly active and reusable heterogeneous catalysts of esterification of fatty acids with methanol and ethanol, Prins cyclization of aldehydes with isoprenol and intramolecular Prins cyclization of citronellal to isopulegol. The catalytic activity of the micro/mesoporous PPCs (TON values up to 522 mol ⋅ mol−1) was higher than that of commercial polymer‐based heterogeneous catalyst Amberlyst 15 possessing gel texture without permanent pores and that of p‐toluenesulfonic acid applied as a homogeneous catalyst.